The present invention relates to a device intended for providing automatic verification of the positioning of a surgical instrument with respect to elements of the body of a patient, and in particular to a device adapted to ensure verification of the positioning of an odontological tool in a radicular canal with respect to the apex of a tooth. The present invention also relates to a process for detecting the apex of a tooth.
It is known that, in surgery, the positioning of an instrument must sometimes be made at a determined place of a given medium, close to a second medium, in an area not visible of the surgeon.
This is the case in odontology where the preparation of the canal must respond to two essential objectives, namely, to extirpate the pulpy tissue and evacuate it from the radicular canal and, secondly, to machine the latter to give it an appropriate shape, adapted to receive a hermetic stop perfectly obturating the canal hermetically up to its terminal part.
For reasons of rapidity and efficiency, this machining is usually affected with the aid of an apparatus comprising a tool, such as a file, which is subjected to vibrations whose frequency lies within the ultrasonic domain.
One problem encountered by the practitioner carrying out such a technique is that of ensuring a clean and quasi-perfect "machining" of the radicular canal of the patient's tooth, while avoiding going beyond the apex thereof, i.e. the constriction located at the bottom of said canal and which separates this latter from the patient's mucous membrane, for fear of causing the patient serious injury.
The means available to the practitioner to ensure such detection are, first conventional localization methods such as tactile sensitivity or radio-graphic monitoring and, second electronic monitoring means.
These latter usually measure the electrical resistance existing between a first electrode, or gingival electrode, placed in contact with the patient's gum, and a second electrode, sometimes constituted by the file itself, which is introduced in the radicular canal, a decrease in resistance at the level of the apical constriction indicating the proximity of the mucuous membrane and therefore of the apex of the tooth.
French Patent 85/17632 discloses an apparatus for monitoring, during the progress of a probe or a tool at rest, inside the radicular canal, the variation of a physical parameter such as conductance, which undergoes a sudden increase when the probe arrives in the immediate proximity of the apex. Once the proximity of the apex is determined; the practitioner then engages on his tool a marking stop generally by an elastic washer which is maintained thereon by friction and which, during the "machining" phase, will enable the to know at what moment his tool will reach the apex.
Although such a device makes it possible to define with high precision the relative position of the tool with respect to the apex, it requires the positioning of a marking stop on the tool. The positioning of the marking stop, precisely by reason of its mode of fixation, is neither precise nor reliable. As an example, the marking stop may shift beyond its initial setting, which during the machining phase, may cause the apex of the tooth to be exceeded.
As an alternative, the intervention is then made in two phases, namely a first phase of measurement and a second phase of actual machining, which involves a loss of time both for the surgeon and for his patient.
Finally, in this type of device, the may be a sudden increase in the conductivity measured by reason of diverse causes, without the tool being in the vicinity of the apex of the tooth, so that there is a risk of stopping the "machining" of the radicular canal before it has arrived at the apex thereof. Of course, to avoid this drawback, the value of the threshold of detection of the apex may be increased but, in that case, there is a risk, during the phase of machining of the radicular canal, of continuing the latter beyond the apex, and into the patient's mucous membrane.